LCD displays are widely used in TVs, laptop computers, PCs, mobile phones, and other electronic products having display function. In an LCD display, cold cathode fluorescent lamp (CCFL), field-effect light-emitting device (EL), light-emitting diode (LED), or other elements capable of emitting a visible light are used as a backlight. In recent years, LED has gradually become a preferred backlight source instead of CCFL because of its various advantages including: long lifetime (about 100,000 hours), capability of optimizing color gamut, small size/design flexibility, low-voltage power supply driven, short turn-on time, no inverter needed, efficiently operated over a wider temperature range and so on.
An LED backlight device comprises an LED matrix for providing an LCD panel illumination, usually. In order to make the LCD panel be illuminated with uniform light, and prevent bright spots being generated by LED backlight device on the LCD panel, using a lens to refract the light from an LED is the mainly solution in prior arts. Therefore, in the LCD display using LEDs as backlight source, the way to enhance the uniformity of brightness or make the light distribution be wider is the main issue for improving the LED backlight device. For example, U.S. Pat. No. 7,348,723, U.S. Pat. No. 7,963,680, U.S. Pat. No. 7,621,657, U.S. Pat. No. 7,798,679, U.S. Pat. No. 7,866,844, U.S. Pat. No. 7,766,530, US Patent Publication No. 20090116245, U.S. Pat. No. 7,474,475, and U.S. Pat. No. 7,746,565, all disclose lenses or LED devices designed for an LCD panel.
A light source device 1 shown in FIG. 1 is disclosed in U.S. Pat. No. 7,348,723. The light source device 1 comprises an optical lens 13 and a light emitting element 11 mounted on a substrate 12. The light emitting element 11 is disposed in a hemispherical recession 10 of the optical lens 13. During operation, a light beam emitted from the light emitting element 11 travels within the optical lens 13 and then passes through a light control emission face 130 of the optical lens 13. The light control emission face 130 includes a first light emitting region 130a and a second light emitting region 130b, in which the first light emitting region 130a has a slightly and downwardly curved convex configuration which curves toward the light emitting element 11. FIG. 2 is a schematic diagram of U.S. Pat. No. 7,348,723 showing an emission intensity distribution of the light source device 1. Therefore, the light pattern forms a round light pattern which includes a paraxial region with higher emission intensities and an off-axis region with lower intensities.
Nevertheless, the light source device 1 has imperfections, termed as “bright dots”, which are found in the paraxial region on the illuminated object. These kinds of issues are unlikely to be overcome due to an uneven distribution of emission intensity of the light source device 1. Moreover, in order to ease the uneven light pattern generated on the LCD panel, a plurality of the light source device 1 in a backlight module have to be arranged closer to each other. Furthermore, because of the increase in demand of thin display and cost reduction, a light source device must be improved to increase the light emission angle thereof. Thus, the distance between the light source device 1 and LCD panel can be shortened, and the distance between each light source device 1 can be increased. However, the light source device 1 improves its scattering property by merely enhancing the refractive power of the light control emission face 130 thereof, such that a Fresnel reflection tends to be generated. That is, the total flux of the light emitted from the light control emission face 130 decreases. In addition, parts of light emitted from the region where the incident angle is equal to the corresponding emission angle, are overlapped thus outgoing light fluxes are concentrated, thereby causing of a ring-shaped bright portion in the light pattern. In a result, the light source device 1 is hard to have a high light-scattering ability and a uniformity of light distribution simultaneously. A light source device disclosed in U.S. Pat. No. 7,621,657 is similar to the light source device 1 disclosed in U.S. Pat. No. 7,348,723, it also has the shortcomings of having bright spots in the paraxial zone thereof and an insufficient scattering ability.
U.S. Pat. No. 7,766,530 discloses a light source device including an optical lens having a light incident surface and a light emitting surface. The optical lens has convex surfaces in an inner portion of each surface, and concave surfaces in an outer portion of each surface, thereby forming a bell shaped lens. However, this type light source device also provides a light pattern with higher intensities in the paraxial region thereof. In addition, such convex surfaces make the incident light be refract to further away from the optical axis; such concave surfaces make the light away from the optical axis of the light source device be refract to further close to the optical axis. Therefore, such light source device also has the shortcomings of uneven light distribution and deficient scattering ability.
U.S. Pat. No. 7,866,844 and US2009/0116245 disclose lenses each comprising a light incident surface having jagged structures and a recession, so as to achieve the goal of heat dissipation and prevention of generation of bright ring. However, optical structures disclosed in the two patent documents also cause a light pattern with higher intensities in the paraxial region thereof. Therefore, the requirements of light distribution uniformity and light scattering ability are hard to meet.
For improving the scattering ability of a light source device, optical lenses of the light source devices are disclosed in U.S. Pat. No. 7,963,680, U.S. Pat. No. 7,798,679, U.S. Pat. No. 7,474,475, U.S. Pat. No. 7,746,565. Each light incident surface of these optical lenses has concave curve to form a recession. In the other hand, each light emitting surface of these optical lenses has a concave part disposed at the center thereof and a convex part disposed peripherally. The optical lens disclosed in U.S. Pat. No. 7,963,680 has the light emitting surface including a cone-shaped recession at center and a light incident surface forming a bullet-shaped recession with round top. A light source device using such optical lens provides a light pattern having lower intensities in the paraxial region thereof so as to get a wider light distribution. However, such optical lens is still hard to use in a thin display due to the limit of its optical structure. In addition, the optical lens disclosed by U.S. Pat. No. 7,798,679 also could distribute the light from a light source device, to provide a wider light pattern having lower intensities in the paraxial region thereof. However, in practical applications, light nearby the optical axis is strongly refracted by such optical lens, such that the light pattern projected by the light source device has a broadened dark area in its center. In a result, such optical lens is not applicable to use in thin displays.
U.S. Pat. No. 7,474,475 and U.S. Pat. No. 7,746,565 disclose light source devices each including an optical lens having complicated optical surfaces. Both the optical lenses comprise a light emission surface having a recessed part rear the optical axis. Wherein, according to a total reflection effect, light incident on the recessed part is reflected to a refracting part that extends from the recessed part and forms a convex shape. By the optical surfaces, such light source devices can provide a light pattern having lower intensities in the paraxial region thereof to make the light distribution become wider. However, such light source devices are unlikely to provide an even light pattern in practice, in the other hand, such lenses are hard to process, and tends to be thicker and low precision as its complex spherical surface.
Broadly speaking, optical surfaces are not portions of a sphere or plane called asphere, including asymmetric free-form surfaces. Because aspherical lenses have significant effects on simplification of optoelectronic devices, and reduction of size as well as weight of optoelectronic systems including optical elements, they have been widely used in various fields according to the optoelectronic devices in recent years.
The optical structure of an LED light source device applied to a thin display is strictly controlled to ensure the uniformity of a light pattern thereof. If LED light source devices applied to a display have design deficiency, they may cause the problems of a bright dot (or a bright ring), chromatism, higher cost due to requirement of high density layout or requirement of disposing other elements for promoting even light distribution. Wherein, when an LED light source device has a problem that the light distribution made by the light source device is too concentrated or too dispersed in the paraxial zone thereof, it may cause chromatism thereby affecting the color rendering of the LCD display. Besides, high density layout of the LED light sources will result in an increment of manufacturing cost, an accumulation of heat and a reduction of the device lifetime. Disposing other elements further leads to increment of volume or weight of the display. Because displays tend to be thinner, be realistic in quality and their cost tends to be minimized, the way to enhance the scattering ability of the LED lens, and reduce chromatism as well as thickness of the LED lens is the main issue that the related manufacturers according to illumination devices are anxious to develop.